as her mother stood in shook (is/needs to be) set off as parenthetical information. If you wanted to be anal you could write it like this: Sylvia opened the front door as her mother stood in shock watching her little girl walk outside. or something like that to make the syntax clearer to the reader.
No. Should read: "As her mother stood in shock, Sylvia opened the front door and walked outside." or "Sylvia opened the front door and walked outside as her mother stood in shock."
As her mother stood in shock which was a deep shock, Sylvia opened the door which was the front door and walked outside which was the opposite of inside.
OP is not grammatically correct. There either has to be a comma after "door" or the comma after "shock" has to be removed. Actually, depends on what you're talking about - is Sylvia walking outside or the mother? It's really best to just rearrange the sentence. Sylvia opened the front door as her mother stood in shock and walked outside.
If you want to use an ellipsis for suspense or continuation, do THREE (3) dots, not FOUR (4). This would not really work as a correction to his sentence because you wouldn't know who walked outside; you wouldn't know who was inside the house, either. It would be best to also have a subject there, as in "It should read...", so that you may have a complete sentence. It's cool and, although it sounds weird to have that dependent clause in the middle, it could be written as dandorotik suggests. You're missing an apostrophe. "Don't" is a contraction of "Do not" and should have an apostrophe.
